Because the ball was actually spotted for the first down and when they reviewed it they determined he was down short. The clock then wound up not being a factor because that last play was 4th down. Even with more time left it's Michigan's ball.
Well Hoke has been doing a great job of recruiting offensive lineman, but you have to remember they're all young at this point. The first real class of his and the one where he first took a bunch of them was the 2012 class. The 2013 class then had even more highly touted guys. But that makes them all either redshirt freshman or true freshman right now at the position that takes the longest to develop.